首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   18293篇
  免费   192篇
  国内免费   329篇
航空   10269篇
航天技术   5375篇
综合类   379篇
航天   2791篇
  2021年   170篇
  2018年   181篇
  2016年   166篇
  2014年   489篇
  2013年   575篇
  2012年   450篇
  2011年   612篇
  2010年   472篇
  2009年   826篇
  2008年   848篇
  2007年   399篇
  2006年   465篇
  2005年   397篇
  2004年   437篇
  2003年   510篇
  2002年   478篇
  2001年   568篇
  2000年   381篇
  1999年   501篇
  1998年   460篇
  1997年   342篇
  1996年   392篇
  1995年   452篇
  1994年   406篇
  1993年   390篇
  1992年   294篇
  1991年   276篇
  1990年   247篇
  1989年   385篇
  1988年   212篇
  1987年   238篇
  1986年   228篇
  1985年   637篇
  1984年   512篇
  1983年   401篇
  1982年   485篇
  1981年   609篇
  1980年   243篇
  1979年   184篇
  1978年   189篇
  1977年   144篇
  1976年   156篇
  1975年   184篇
  1974年   181篇
  1973年   161篇
  1972年   188篇
  1971年   148篇
  1970年   143篇
  1969年   147篇
  1967年   142篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
841.
The steady-state weight vector derived by either the least mean square (LMS) or normalized least mean square (NLMS) algorithms has random deviations from the optimum values. These deviations increase the steady-state residue power. A previous paper derived the LMS weight noise effects for a multiple sidelobe canceller (MSLC) application. This paper describes the NLMS weight noise effects. It is shown that for a thermal noise environment, the weight noise effect for the LMS algorithm is insignificant but is quite significant for the NLMS algorithm. Calculations for example noise plus interference environments imply that the NLMS weight noise effects are always larger than that for LMS.  相似文献   
842.
Time of arrival (TOA) estimation of narrowband signals is a problem of considerable practical interest in radar and sonar applications. A new technique is presented to analyze the mean square error (MSE) performance of TOA estimation schemes, based on recently developed lower bound. We obtain a complete characterization of the MSE as a function of the signal and noise parameters. The results are given in a simple closed-form analytical expression.  相似文献   
843.
Analysis based on the state-plane diagram is given for series resonant converters operating in the frequency range 0.5 ? fs/fo ? 1.0. When the voltages and currents in the converter are normalized, design parameters take on special geometric meanings in the normalized state diagram. Examples of converter design using graphical methods are given for the cases of ? and ? control. Control characteristics of the converter operating in the continuous conduction mode are derived. The concept of the energy reflection coefficient is introduced as a measure of power transfer efficiency in the converter design.  相似文献   
844.
An adaptive antenna array is defined as an antenna array whose output is the weighted sum of the signals received at the antennas, with signal-dependent automatic adjustment of the weights to optimize some criterion. This open-literature bibliography of papers on the subject is intended to provide a brief overview of the field, and the authors involved, up to the end of 1985. Papers are listed both by subject area and by sole/primary/secondary author.  相似文献   
845.
This note deals with the effect of the common process noise on the fusion (combination) of the state estimates of a target based on measurements obtained by two different sensors. This problem arises in a multisensor environment where each sensor has its information processing (tracking) subsystem. In the case of an ?-? tracking filter the effect of the process noise is that, over a wide range of its variance, the uncertainty area corresponding to the fused estimates is about 70 percent of the single-sensor uncertainty area as opposed to 50 percent obtained if the dependence is ignored.  相似文献   
846.
847.
Book review     
  相似文献   
848.
Current information on the neutral atmosphere of Jupiter is reviewed, with approximately equal emphasis on composition and thermal structure on the one hand, and markings and dynamics on the other. Studies based on Pioneer 10 and 11 data are used to refine the atmospheric model. Data on the interior are reviewed for the information they provide on the deep atmosphere. The markings and dynamics are discussed with emphasis on qualitative relationships and analogies with phenomena in the Earth's atmosphere.Contribution No. 2652 of the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, Calif. 91125, U.S.A.  相似文献   
849.
In [1] a scheme for forming a rectangular FIR filter bank is described using only a few percent of the number of multiplications required by straightforward procedures. The sidelobe level suffers degradation. Attention is drawn to a different scheme published in [2] and [3] which needs even fewer multiplications without degradationvof the sidelobe level.  相似文献   
850.
This paper demonstrates and tests a new algorithm for extracting velocity information from a pulse Doppler radar signal. The system is adaptive and performs weil in the presence of target scintillation. This paper also shows a special steady-state version of the adaptive algorithm. lt is computationally attractive and produces near optimal velocity estimates.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号